Why brushless (inrunner) motors aren't best for crawling

[colebz]

Originally Posted by nigels_world

Do you have any video of the startup from a stop on a downhill?

No. I will get one next time I go out, though. Should be in the next day or so. Its raining pretty hard. Or maybe I'll just do it inside on a chair or something. We'll see how clean the tires are. lol
I will get one up soon! :thumbup:

[Calderwood]

Originally Posted by colebz

No. I will get one next time I go out, though. Should be in the next day or so. Its raining pretty hard. Or maybe I'll just do it inside on a chair or something. We'll see how clean the tires are. lol
I will get one up soon! :thumbup:

It's been raining here too. How many cells do you run the 6 pole motor on? Does the esc get hot from how fast it switches?

[colebz]

Originally Posted by nigels_world

It's been raining here too. How many cells do you run the 6 pole motor on? Does the esc get hot from how fast it switches?

I run 2 and 3 cell, but mostly 3 cell. I have noticed very minimal heat build up on the esc and motor. They are both barely warm to the touch after 4 hours of a mix of rock crawling (bouncing) and hill climbing.

[stevem50]

what motor are you running?

[cerpindicular]

my first crawler was a scorpion i traded for that had 1000kv outrunner in it and i loved it had tons of torque and no cogging esc/motor where cheapy hobbypartz or hobbyking i can't remember now. I now have a brushed scx-10 running a old ae-1 esc and a traxxas titan and it has a terrible problem with cogging at low speed. I think as long as the kv is low the cogging becomes less of a issue. Also while i waterproofed the servo/esc/battery/deans connector i never touched the outrunner and I frequently dunked the whole truck a few time to the point where it was more submarine then truck. I think it really does just come down to cleaning/oiling on brushless motors after your done.

[colebz]

Originally Posted by stevem50

what motor are you running?

http://www.hobbyking.com/hobbyking/s...or_1900KV.html
Sorry, but I was wrong. It's not a 6 pole motor. I swear it said 6 poles when I bought it lol. Anyway, it works great! I'll shoot some video tonight.

[panama]

Originally Posted by Duuuuuuuude

My latest attempt was with an LT4. They behave way, way differently.

I love my LT4 and yes they seem to work well either way sensored or non.

[stevem50]

i was wondering... all the times i read it , i have never seen a 6 pole hobby motor, but if they existed i wanted to find out more. haha

[stevem50]

that is a big bastard you had a link to colebz, wish there was room in my wraith for something with that much power. i would have to cut out half my chassis to fit it. funny thing about motors like that... after all this cogging talk, that thing would rip a wraith in half or twist a scx chassis up like a pretzel before it stalled. oh yeah... a 35t brushed motor has way more power than that... haha, my a$$

[88RRC]

Originally Posted by stevem50

i was wondering... all the times i read it , i have never seen a 6 pole hobby motor, but if they existed i wanted to find out more. haha

They exist, Tenshock makes one. They also have an 1/5 scale 8 pole too. I can't imagine how brutal those things are. I'm running one of their 4-Poles in my Yota and it's wicked fast and has torque out the wazoo.

Link:Tenshock 6-Pole

Ben

[stevem50]

monsters i say... damn monsters. my driveshafts are crying and hiding in the bottom of my toolbox now that they know these killers are running around free

[colebz]

Well, I have a video uploading. sorry for the delay. Im driving with one hand and filming with my phone in the other. It is very cold and I was having a hard time finding a place with enough traction, so it wouldn't slide. The dragbrake was locking up the tires, causing it to slide down. So, I put the dragbrake on 80% and tried to make it as steep as I could. After turning the dragbrake down, it wouldn't hold itself up, so I had to make a "step" on the incline. Watch the video and you'll get it. Lol
it is a big motor, but all I did was shim under the tranny a few millimeters, trim a small amount off one of the upper link mounts, and did some minor interior trimming. Motor fits on stock motor plate with 56/15 32p gearing. I got a new interior, so I cut up the one in my truck to see the best way to go about it. The place that needs trimming is between the center console and the passenger seat. the seat covers the area that needs trimming, so nobody will notice it is trimmed.:thumbup:

[colebz]

Here you go. Let me know if this is what you wanted. I am just getting used to the 4pl in my wraith. Only had it in the past couple runs and the throw is way different than a traxxas tx, lol.
Is there a sensitivity adjustment for the throttle on the 4pl?
https://www.youtube.com/watch?v=P1G7...e_gdata_player
Also, an example of how slow it can go forward, uphill http://m.youtube.com/watch?feature=m...&v=7GBfL6levwQ

[Nova's Ark]

Gear down and volt up, especially with brushless.
Sensored in runners are awesome.
Non sensored is a different story.


4S Lipo
castle creation BEC
Tekin 13.5 motor sensored inrunner
96tooth spur
17 tooth pinion
That is one of the best and most copied formulas to make a solid RC rock crawler.

Non sensored can be made to work, but gearing, voltage and programming of ESC are key.



Sent from the lab @ the CI compound

[The Violator]

Originally Posted by Meatwad

I'm a fan of sensored brushless setups, but they will never be as smooth as their brushed counterparts. The free rolling period between application of throttle, letting off throttle and drag brake always kills me. If there can be a variable drag brake option similar to the cheat function of the castle systems, then this would be a non issue.

For normal trail running, these are non issues for the most part. During actual crawling however, these can be deal breakers for some.

It seems everyone kind of ignores this. IMO, a pro4 3300 is about perfect in a scaler. Butter smooth, lots of power. But on a down hill, add a little throttle and it takes off rolling down the hill. On my 1.9 comp car I ran the losi brushless system and it was a powerhouse until you went down hill. I ended up using plastic wheel hexes that I could over tighten to add the friction to keep it controllable on the down hills. That is one hell of a band aid. The ESC need some kind of servo type control that can hold it from free rolling.

[Calderwood]

Originally Posted by The Violator

It seems everyone kind of ignores this. IMO, a pro4 3300 is about perfect in a scaler. Butter smooth, lots of power. But on a down hill, add a little throttle and it takes off rolling down the hill. On my 1.9 comp car I ran the losi brushless system and it was a powerhouse until you went down hill. I ended up using plastic wheel hexes that I could over tighten to add the friction to keep it controllable on the down hills. That is one hell of a band aid. The ESC need some kind of servo type control that can hold it from free rolling.

The down hill issue is the biggest problem for brushless motors. I have thought about putting a 1/8 scale style disk brake on the back of the tranny and then use the radio to mix in a little brake at low-zero throttle positions.

[JohnRobHolmes]

Originally Posted by Calderwood

The down hill issue is the biggest problem for brushless motors.

It isn't the motor's fault, it is the ESCs fault that they freecoast on downhills. While some brushless motors don't exhibit the free coast, like outrunners, inrunners will typically freewheel away as soon as throttle is given. Brushed motors don't freecoast because of the brush drag, making them inherently a superior choice for drivers that compete in gate style comps.


There are commutation schemes that prevent freecoasting on brushless motors. The problem is that most ESCs on the market don't have the processing power to handle it. I haven't found a manufacturer willing to modify (or let me modify) the code to such extent either, nobody making hobby controllers is familiar with anything except basic six-step or sine commutation styles. You may hear engineers say "We can't have throttle and brake at the same time!". This is inherently false, what they mean is that they are unwilling or uneducated enough to pursue beyond duty cycle modulation of speed.

All is not lost on affordable prevention of brushless motor freecoast though. The Revolver S sensored outrunner mitigates it with design. There are also other control schemes we are working on that do not increase processor overhead, but they are tied to sensored only commutation and cannot perform the task in sensorless mode. I've been working on this for a few years now, it is a slow process to crack open ingrained industry practices while keeping final cost the same.






Low speed control is another issue altogether. Sensored or brushed is the only way to go for best control. If you can run sensorless without issue, you just aren't getting the rig bound down enough to matter and you don't need low speed resolution enough to matter.

Motor design plays a large part in low speed control, at least with the dumb as a brick six-step commutation hobby ESCs have. Smoother spinning motors will have better startup control, but sacrifice drag brake and free roll. Increasing the pole count mitigates free roll by decreasing the ohmic resistance and inductance for a given KV of motor- allowing faster collapse of the magnetic field between commutation steps. Increasing ESC and battery size also reduce free roll while increasing drag brake in the same way. Less circuit resistance = higher drag and faster regulation of motor speeds.



So when it boils down to it, the problems some have with brushless are because the ESCs are made with minimal engineering and parts costs. Some motors just show the shortcomings more than others.

[6sharky9]

ESC makers have to save something for the future with programming..they know they can be more capable but if they give it all to us now it gives them no time for more development for the future.....Very very hard to beat a brushed motor for low rpm and always will be till the makers decide to step it up...But from a cost stand point I don't see brushed taking a backseat to a brushless set up for a long long time when it comes to low rpm scenarios

[colebz]

Originally Posted by JohnRobHolmes

It isn't the motor's fault, it is the ESCs fault that they freecoast on downhills.

Thanks for the input. That makes a lot of sense. I dont think my video is the best example, but im trying to show that my setup doesn't "free roll" much at all. The board is slick and my wraith slides a couple times. Also, I am not used to the sensitivity on my 4pl. I had a traxxas 2.4 with the sensitivity turned all the way down and it was a lot easier to control on the low end. I think the settings on your transmitter, make a big difference! I don't have the same "resolution"when I use the 4pl, or it is not setup right. I just found the sensitivity setting, so I will adjust it and see how it is.

[Calderwood]

Originally Posted by JohnRobHolmes

It isn't the motor's fault, it is the ESCs fault that they freecoast on downhills. While some brushless motors don't exhibit the free coast, like outrunners, inrunners will typically freewheel away as soon as throttle is given. Brushed motors don't freecoast because of the brush drag, making them inherently a superior choice for drivers that compete in gate style comps.


There are commutation schemes that prevent freecoasting on brushless motors. The problem is that most ESCs on the market don't have the processing power to handle it. I haven't found a manufacturer willing to modify (or let me modify) the code to such extent either, nobody making hobby controllers is familiar with anything except basic six-step or sine commutation styles. You may hear engineers say "We can't have throttle and brake at the same time!". This is inherently false, what they mean is that they are unwilling or uneducated enough to pursue beyond duty cycle modulation of speed.

All is not lost on affordable prevention of brushless motor freecoast though. The Revolver S sensored outrunner mitigates it with design. There are also other control schemes we are working on that do not increase processor overhead, but they are tied to sensored only commutation and cannot perform the task in sensorless mode. I've been working on this for a few years now, it is a slow process to crack open ingrained industry practices while keeping final cost the same.






Low speed control is another issue altogether. Sensored or brushed is the only way to go for best control. If you can run sensorless without issue, you just aren't getting the rig bound down enough to matter and you don't need low speed resolution enough to matter.

Motor design plays a large part in low speed control, at least with the dumb as a brick six-step commutation hobby ESCs have. Smoother spinning motors will have better startup control, but sacrifice drag brake and free roll. Increasing the pole count mitigates free roll by decreasing the ohmic resistance and inductance for a given KV of motor- allowing faster collapse of the magnetic field between commutation steps. Increasing ESC and battery size also reduce free roll while increasing drag brake in the same way. Less circuit resistance = higher drag and faster regulation of motor speeds.



So when it boils down to it, the problems some have with brushless are because the ESCs are made with minimal engineering and parts costs. Some motors just show the shortcomings more than others.

John, can you wind a ~3500kv Revolver S?